The present invention relates to the preparation of oxophthalazinyl acetic acids having benzothiazole or other heterocyclic side chains. Such compounds function as aldose reductase inhibitors and are useful in the treatment of certain chronic complications arising from diabetes mellitus, such as diabetes cataracts, retinopathy and neuropathy. Such compounds are disclosed in U.S. Ser. No. 263,577, filed Oct. 27, 1988, the disclosure of which is hereby incorporated herein by reference.